<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script>
  // 实现 (5).add(3).minus(2) 功能
  Number.prototype.add = function(num){
    return this + num
  }
  Number.prototype.minus = function(num){
    return this - num
  }
  console.log((5).add(1).minus(2))
</script>
</html>